The present invention relates to balanced speaker systems and, in particular, to a speaker enclosure having an exterior wall with an elliptically-shaped opening formed therethrough, with the edges of the opening being tapered to cause air pressure waves to exit therefrom in a cone-shaped pattern, and acoustically balanced transmission yolk mounted thereto for relieving interior pressure and augmenting the bass range of the speaker without distortion or dampening at frequencies of 60 hertz and lower.
The integrity and quality of sound transfer systems is especially linked to speaker performance, since no matter how faithful a sound is recorded or replayed, distortion induced at the speaker still ruins the sound. While most recording systems do record and replay sounds rather faithfully for the mid-range frequencies, their performance tends to fall off at the upper and lower ends of the audio frequency range. Thus, it becomes especially important that any speaker system associated with any sound transfer system be responsive to this frequency roll off, without inducing any undesired distortion or extra sounds of its own or adding significantly to system losses.
Relative to woofer speakers, this becomes even more important, since the bass notes, through their low frequencies and high power output, due to their large surface speaker cones, tend to dominate over other frequencies and thus any speaker induced distortion tends to become rather pronounced relative to the listener. Also, because of the inherent driver losses at these low frequencies, the reproduced frequencies and sounds are not as full or complete as they should be. It is, therefore, desirable that for any system having a variety of speakers accomodating various frequency ranges that the bass speakers or woofers be able to augment the power losses of the driver without adding sounds of their own, creating interference, sympathetically resonating or otherwise distorting the sound.
Heretofore, a variety of speaker systems; including tubes, horns, labyrinths, transmission lines, screens, sub-woofers, etc., have been developed for faithfully reproducing recorded sounds and which most popularly have included the "infinite baffle" system wherein a completely sealed speaker enclosure contains the speaker that accommodates induced interior pressures without adding great distortion to the sound. Such speakers, however, suffer from a rather fast roll off at low frequencies and do not induce the high energy content sounds such as are required for frequencies of 60 hertz or less.
Theatre speakers, on the other hand, through various structural modifications, couple a portion of the back-pressure-wave induced by the speaker to a horn, a labyrinth or another passive radiator or speaker cone, the output of which augments the driven speaker. A problem attendant with such speakers, however, is high distortion and storage time which makes such speakers unsuitable for systems requiring high fidelity. Such speakers are efficient, however, and therefore may be used for public address systems or the like.
Additionally, the bass speaker of the present invention differs from known ported speakers in that in lieu of a circular or square port and a sound collecting tube, it employs an elliptical window which creates an air cone as pressure waves driven by the woofer exit therefrom. Also, an ellipsoidal or wedge-shaped cavity is positioned relative to the elliptical window and possesses a balanced acoustical transmission yoke. Internal speaker enclosure pressure waves are thus collected at the shaped gates opening to the transmission yoke, are formed and then transmitted through the elliptical window with less storage time to reinforce the reproduced sound at the frequencies of operation for which the driver equipment output begins to fall off. Furthermore, the window size and position are selected such that at the selected frequencies of operation, the elliptical window is operative to augment the generated sound in a real time fashion and in time-phase with the speaker's generated sound, thereby avoiding lost sounds or out-of-phase sounds inherent in the tube connected ported speakers. The window is also large enough so that a meaningful output is obtained thereby.
The speaker of the present invention is thus intended for combination in a system of speakers, where the present enclosure is typically used in conjunction with the woofer, while a mid-range speaker and tweeter are successively stacked thereabove. Appropriate bandpass filters separate the speakers and ensure operation at the proper crossover frequencies. For the woofer, a passive crossover with the oval window occurs at 60 hertz while the crossover with the mid-range driver occurs at approximately 130 hertz and while the tweeters crossover at 2,700 hertz. Each speaker, in turn, is separated from the other and the floor via a mat having a linear sound transfer function such as the Fulton Kinetic Barrier.TM. sound transfer mats sold by Fulton Musical Industries of Minneapolis, Minn.
The speakers of the preferred embodiment are also fabricated with a high mass, sound augmenting enclosure. In particular, the enclosures are comprised of a front escutcheon having a speaker opening bored therethrough and an underlying shaped ovaloid window mounted along the same axis as the woofer opening. An ellipsoidal or wedge shaped chamber, formed in a balanced acoustical transmission yoke, is mounted behind the elliptical window interior to the otherwise airtight speaker enclosure and is operative in a push-push fashion at frequencies below 60 hertz so as to augment the produced sound and thereby extend the range of frequency response for the speaker, without inducing additional distortion.
System operation is, in turn, enhanced due to the augmented bass response, lower crossover frequency and real time response characteristics of the present woofer. Complex sounds, such as are produced by symphonic orchestras, can now better be distinguished, since the bass sounds do not override the upper bass and midrange tweeter. The system's dynamic range is also wider and each instrument is better distinguishable from one another without "smearing", while bass power remains intact so as to permit the playback of the sounds at the same power levels as originally played.
The above objects, advantages and distinctions of the present speaker enclosure and system as well as various others will, however, become more apparent upon reference to the following description of the preferred embodiment thereof with respect to the following drawings. Before referring thereto, though, it is to be recognized that the following description is made with respect to the presently preferred embodiment only and thus various modifications (over and above those mentioned) may be made without departing from the spirit and scope of the present invention.